This invention pertains to tire retreading operations of the type wherein a flexible envelope member is used to form a fluid-tight enclosure about a replacement tread strip encircling the circumferential surface of a used tire and adapted to be permanently bonded thereto during treating of the aforesaid assembly within a heated pressure chamber. The invention more specifically relates to the manner of achieving the necessary fluid-tight, sealed condition of the envelope enclosure.
It is well known that, in tire retreading operations of the foregoing type, a satisfactory permanent bond will not reliably ensure between a replacement tread strip and a tire to be retreaded if air and/or other fluid is present in the bonding region between the strip and the tire during the treatment thereof within a heated pressure chamber. It is also known to form an enclosure about such region by means of a flexible envelope having venting means associated therewith by which air or the like can be evacuated once the necessary fluid-tight sealed relationship of the envelope about the region has been established. The prior art suggests a number of different ways of achieving the necessary fluid-tight sealed condition of the flexible envelope. One such way is by the use of mechanical clamping devices having thereon opposed clamping surfaces between which marginal edge portions of the envelope are secured: See, e.g., U.S. Pat. Nos. 3,966,535, 3,846,201 and 3,802,978. This technique is highly reliable, in that realization of the desired fluid-tight sealed relationship is not dependent upon the particular surface characteristics of the tire to be retreaded or upon a precise relationship between the size of the envelope and the size of the tire. However, clamping devices of the aforesaid kind are relatively expensive to acquire, maintain and use: In the latter regard, their use-cost is particularly high when the clamping devices are so constructed as to not permit retreading of a tire while the same is mounted upon the customer's rim, but rather requires de-mounting of the tire from such rim prior to the retreading operation, and subsequent re-mounting of the tire upon such rim following retreading.
Another prior-art envelope-sealing technique involves mechanically clamping one or more portions of the envelope against one or more surface portions of the carcass of the tire to be retreaded: See, e.g., U.S. Pat. Nos. 2,976,910 (FIGS. 1-6 embodiments), 3,779,832, and 3,884,740. While certain devices employing this technique may be somewhat less expensive to acquire, maintain and use than devices of the first type described above, they do not as reliably establish the necessary fluid-tight sealed condition of the envelope and, in some instances, require the use of specially-designed heated chambers which are capable of accommodating only a single tire at a time. It is of course much more economical and desirable, in the latter regard, for the envelope sealing means to be of such nature as to permit a number of tires to be simultaneously treated in a heated pressure chamber of large room-like construction.
U.S. Pat. No. 3,769,121 discloses the retreading in a chamber of the above-described type of a tire enclosed by a flexible envelope which extends completely about the tire carcass and the replacement tread strip thereon, and which has its marginal edge portions in overlapped relationship to each other. A similarly-constructed and arranged "full-wrap" envelope is disclosed in U.S. Pat. No. 2,966,936. Apart from the questionable reliability of the seal achieved thereby, the foregoing arrangement cannot be used for the retreading of a tire mounted upon the customer's rim, and requires utilization of a relatively large envelope of special design and construction.
Use of a smaller-size envelope, apparently without the accompanying use of any clamping device or means, is disclosed in U.S. Pat. No. 3,976,910 (FIG. 6a embodiment) and in British Pat. No. 746,375. Although the British patent states that "wetting of, or the application of a little adhesive to the surfaces . . . will be found to improve the seal," primary reliance for the establishment of a sealed relationship between the envelope and the tire sidewalls apparently is predicated, in the tire-retreading methods of both patents, upon a tight contractive fit between the envelope and the components enclosed by it. Such arrangement necessitates a retreader's acquisition, maintenance and selective use of a large number of envelopes whose sizes are closely correlated to all of the different-sized tires to be retreaded. Further, each of the envelopes must possess a high degree of resilient contractability and, unless frequent replacement is envisioned, should be capable of retaining such property even after undergoing repeated heating during use. Considerable expense would be entailed in the acquisition of envelopes of the foregoing type and, since each would have to be stretched into place, in their use. Furthermore, the sidewalls of a tire to be retreaded frequently have irregular surface portions, due either to "gouges" or the like arising from prior use of the tire, or due to the presence of molded size-indicia or other lettering thereon. It is highly doubtful that the retreading technique of the patents would produce a sealed relationship between the envelope and a tire having irregular sidewall surfaces even if the envelope were tightly stretched, and even if the confronting surfaces of the envelope and tire sidewalls were "wetted" or had "a little adhesive" applied thereto.
Commonly-owned and partially-corresponding U.S. Pat. No. 3,689,337 and British Pat. No. 1,277,642 relate to a chamber-type of retreading process wherein a preliminary connection is made, in the vicinity of each lateral edge of an intervening layer of binder material, between the replacement tread strip and tire components of an assembly thereafter subjected to chamber treatment. In the first embodiment of the patents the preliminary connection is made by use of a heating ring which effects vulcanization of the edges of the layer of binder material and which, prior to its aforesaid usage, is employed to mechanically clamp an enclosing envelope or sheet against the tire. Additional embodiments disclose or suggest effecting the desired preliminary innerconnection of components in other ways, some of which entail use of one or more "sheets," "foils" or "covers" which are "bonded," "glued," "welded" or "molded" in place. In each instance, however, the desired preliminary innerconnection of the components of the assembly is apparently completed in all respects prior to commencement of the assembly's treatment within the heated pressure chamber.
U.S. Pat. Nos. 3,904,459 and 3,989,563 are directed to obviating the use of a flexible envelope in chamber-type retreading operations. They advocate, to this end and among other things, securing the replacement tread strip upon the outer circumference of a tire to be retreaded by means of a layer of binder material which, due to preheating and/or a special composition, has a greater plasticity than the conventional cushion gum binder normally used in tire retreading operations. The patents correctly state that the conventional binder material lacks sufficient plasticity at ambient room temperatures to adequately fill all air-entrapping depressions which might be present within the surfaces of a tire to which the material is applied. Although the patents are directed as previously noted to elimination of the use of a flexible envelope or "evacuation jacket" in the tire retreading operation, such an envelope or jacket is disclosed in one embodiment: However, the manner of achieving sealed relationships between the marginal edges of the envelope or jacket and the underlying sidewalls of the tire carcass is not indicated.
Other prior U.S. patents of possible relevance to the present invention are U.S. Pat. Nos. 3,935,045, 3,895,985, 3,894,897 and 3,793,116.